i think for a long time it was "mutually assured destruction" - neither party nor most of their voters could countenance any kind of deviation, as it would ensure that the other side won. politics in the US has been motivated far more by hostility to the other side than by anything positive or constructive, for some time now. but Trump might change this - it's very hard to see the Republicans putting the toothpaste back in the tube again, so to speak - they won't be able to just impose Jeb! ever again.
but if they break up, it would create much more space for democrats who have to hold their noses every four years to do the same
Agreed.
That whole ¡Jeb! thing is what blew the whole thing up. The money guys who pushed that fantasy from the country club set were the ones who showed the country that the GOP as currently established was past hope. Trump was the one who saw the open door, and he rode the escalator down from his executive suite right through it. Without Jeb in the mix (and I'm convinced he never really wanted to run, but did it out of "duty" to the family), Rubio would have won the nomination and the election, mainly because he would cut deeply into Hillary's base of women and Latinos.
The others took each other out while Trump strode through them like Robocop gunning down the guilty and the innocent, with the power of the press pushing him over the finish line. He was good for ratings, and now they are scared of the monster they have created/enabled. The DC establishment (both parties) is so opposed to every ounce of Trump's being that it will lock things up completely for the next four years, which is the best possible outcome of the ones we are currently offered. Neither of these will offer for another term in office, imho.